The'magnetic signal'that combines both the induced (J i ) and the remanent (J r ) magnetization is widely used in archaeological and pedological prospecting. Magnetic prospecting recording the lateral variations of the total magnetization is the most frequently used measurement before in-phase magnetic susceptibility (K ph ) and magnetic viscosity (K qu ) mapping. The work presented here brings together three types of prospecting technique: magnetic field survey and electromagnetic measurements with both frequency and time domain devices that measure magnetic susceptibility andviscosityrespectively.The site studied, the Gallic town of Levroux (Indre,France), isparticularly interesting because it includes features such as pits and ditches dug into the calcareous substratum partly filled with topsoil and with residues of different metallurgical and fire activities.The field results indicated anomalies with different types of characterization: (i) many compact features filled with magnetic, electrically conductive and minimally viscous materials; and (ii) elongated anomalies characterized by lower magnetic properties and electric conductivity but relatively higher magnetic viscosity than those of the compact features. In addition to the location of the features, the combination of the information brought by the different types of measurements allows us to evaluate the possible erosion of their upper parts by ploughing, to assess their depth (never deeper than1.30 m) and to precise the nature of the feature's fill.
Interpretation of shallow EMI resistivity and magnetic susceptibility measurements using rapid 1D/3D inversion Short title: Rapid1D/3D inversion of shallow EMI
Complex magnetic susceptibility is a well-known property both theoretically and experimentally. To achieve this measurement, different ways have been tested, like TDEM or multi-frequential measurement on soil sample. In this study we carry out the measurements by the use of a multi-frequential EMI Slingram instrument to collect data quickly and in-situ. The use of multi-frequency data is also a way to correct effects of the conductivity on the in-phase component and effects of the magnetic susceptibility on the quadrature component of the raw signal.
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